An Equivalent-Circuit Modeling of High Impedance Surfaces Employing Arbitrarily Shaped FSS

In this paper deals, an equivalent circuit model of high impedance surfaces (HIS) employing arbitrarily shaped frequency selective surfaces (FSS) is presented. The conventional modelization of the HIS based on the averaged expressions for FSS impedance reveals sufficiently accurate both for normal and oblique incidence for simple FSS shapes, such as patches, and for suitably thick dielectrics. Here a simple model able to predict the behavior of high impedance surfaces comprising arbitrary FSS shapes is presented. The present model assumes a preliminary analysis of the FSS in freestanding configuration for retrieving the equivalent L and C parameters of a certain FSS geometry. In the paper, the variations of the FSS inductance and capacitance are analyzed when a thin substrate is employed. In particular, it is interesting to observe how the FSS capacitance and inductance are modified for thin substrate where the conventional transmission line approach fails. This analysis allows to define a range of validity of the formulations available in the literature.